We finally got Ivy's allergy test results back and it's 100% environmental - trees, grasses, dust mites, and plants (so many that it would probably be quicker to tell you what she isn't allergic to!) We're going to start her on immunotherapy soon and it's a lifelong treatment, but I'm just glad we got to the bottom of it and there is a treatment avaliable.
Just wanted to provide an update in case anyone else is going through this.